Environmentally friendly fuels, e.g., alternative fuels to hydrocarbon-based energy sources, are currently of great interest. Hydrogen is a fuel which is prominent as an alternative fuel and the subject of considerable research effort directed to making it commercially competitive with hydrocarbon-based fuels. However, hydrogen is volumetrically inefficient to store and transport. For compact storage, hydrogen must be compressed to high pressure and stored in specialized tanks. For example, current systems may store hydrogen under 5,000 or 10,000 psi pressure. However, at 10,000 psi the hydrogen storage density is only 0.035 g/cm2. Consequently, storage of hydrogen under high pressure is inefficient.
Hydrogen can be stored in liquid form at very low temperatures, but such storage is energy inefficient because a portion of the available energy of the system must be consumed in the liquefaction process. Moreover, liquid hydrogen is highly volatile and losses of the stored liquid hydrogen due to boil off are considerable and thus storage and transport as a liquid is ineffective to serve as an efficient fuel supply especially for utility to supply a commercial vehicle.
As a result, other methods to store and transport hydrogen are under investigation. Chemical hydrides have been proposed as effective hydrogen storage materials for a variety of applications in both distributed power generation and transportation applications. In particular, complex metal hydrides, such as borohydrides or alanates are of interest as materials for storage of hydrogen in the solid state. The theoretical hydrogen volumetric storage capacity in lithium borohydride is approximately 0.12 g/cm2, more than twice the density of gaseous hydrogen under 10,000 psi.
The goal in the study of hydrogen storage materials is to develop candidates that possess high gravimetric hydrogen storage potential. Chemical hydrides, including alkali metal hydrides, alkali metal aluminum hydrides and alkali metal borohydrides, generate hydrogen through a hydrolysis reaction in water resulting in gravimetric hydrogen densities that range from 9 to 25 weight percent of the hydride. When the waters of reaction and solvation are taken into account, the combined hydrolysis systems have gravimetric hydrogen densities that range from 4 to 9 wt. percent.
Although current reported research efforts are focused on enhancing the gravimetric storage density and lowering the dehydrogenation and hydrogenation thermal barriers in the metal hydrides, the systems under investigation are far from achieving sought storage capacity targets due to high temperatures which are required to release the chemically bonded hydrogen, the slow kinetics of the release reaction, potential formation of harmful fuel cell contaminants and irreversibility under moderate hydrogenation conditions of these systems.
For example, Vajo et al. (Journal of Physical Chemistry B letters, 109, 3719-3722, 2005) showed that combining lithium borohydride and magnesium hydride at 2:1 molar ratio, respectively allowed for reversibility of lithium borohydride at lowered temperature compared to the neat compound and attributed this to the formation of magnesium boride following dehydrogenation of this system. However, the decomposition of magnesium hydride and lithium borohydride occurred at discreet decomposition temperatures that were expected from the neat compounds and no decomposition or destabilization was observed or reported. Also, reversibility was achieved only under severe conditions of 100 bar H2 at 230° C. and the reversibility was extremely kinetically limited.
WO Publication No. 2007/096857 to Goldstein et al. describes a solid phase hydrogen-generating system utilizing a solid chemical hydride fuel selected from the group consisting of sodium borohydride, lithium borohydride, magnesium hydride and calcium hydride. The fuel is encapsulated in a plurality of removable capsules which are pumpable and have a major axis of up to 40 mm. The described fuels include water-soluble borohydrides such as sodium borohydride, and certain water insoluble hydrides including magnesium hydride and calcium hydride. The fuel is in a solid phase form encapsulated with polymers such as rigid or flexible plastics, metals, elastomers, water soluble plastics, resins, waxes, oxides or gels. Silica oxide is listed as an example of an oxide.
U.S. Pre-Grant Publication No. 2010/0108543 to Tokiwa et al. describes a resin composition including a curable silicone resin and a hydrogen storage alloy powder. The hydrogen storage powders are mixed metal alloys.
U.S. Pre-Grant Publication No. 2009/0302269 to Choi et al. describes a controlled foaming composition of hydrogen releasing materials. The foam suppression reagent may be any of celluloses; starches; siloxane polymers; polyvinylalcohols; polyvinylidenes; polypyrroles; polylactones; polycarbonates; polystyrenes; and polysaccharides. Described as hydrogen releasing materials are ammonia borane and lithium borohydride.
U.S. Pre-Grant Publication No. 2009/0060833 to Curello et al. describes a gel form of solid borohydride fuels, having a solid metal hydride and catalyst formed into a single solid member, which is inserted into the gel. The gels are based on a wide list of vinyl polymers including a vinyl-terminated polymethylsiloxane.
U.S. Pre-Grant Publication No. 2008/0220297 to Sarata et al. describes a hydrogen generator containing a complex hydride such as sodium borohydride and a catalyst. A silicone-based anti-foaming agent may be incorporated as an anti-foaming agent.
U.S. Pre-Grant Publication No. 2008/0138674 to Pez et al. describes an apparatus for dispensing a solid fuel carrier to a recipient vehicle. A lanthanum nickel hydride (LaNiH5) silicone oil slurry solid fuel is referenced.
U.S. Pre-Grant Publication No. 2007/0243431 to Zhu et al. describes hydrogen-generating, solid fuel cartridge. Borohydrides including aluminum borohydride are described as a hydrogen generator.
U.S. Pre-Grant Publication No. 2005/0175868 to McClaine et al. describes a slurry composition containing a carrier liquid; a dispersant; and a chemical hydride. The carrier liquid includes an organic liquid such as a light mineral oil. Lithium hydride, lithium borohydride, lithium aluminum hydride, sodium hydride, sodium borohydride, sodium aluminum hydride, magnesium hydride, and calcium hydride are listed as chemical hydrides.
U.S. Pat. No. 7,790,013 to McClaine et al. describes metal hydride slurry of magnesium, magnesium hydride, a carrier liquid and optionally, a dispersant. The carrier liquid could include fluorinated hydrocarbons, such as perfluorodecane, silicone based solvents, saturated organic liquids, such as undecane, iso-octane, octane and cyclohexane, or mixtures of high boiling point hydrocarbons such as kerosene.
U.S. Pat. No. 7,594,939 to Goldstein et al. describes a solid phase hydrogen-generating system utilizing a solid chemical hydride fuel selected from the group consisting of sodium borohydride, lithium borohydride, magnesium hydride and calcium hydride, wherein the fuel is encapsulated in a plurality of removable capsules.
U.S. Pat. No. 7,052,671 to McClaine et al. describes a composition comprising a carrier liquid; a dispersant; and a chemical hydride for use in a hydrogen generator. The carrier liquid includes a mineral oil, e.g., a light mineral oil and the composition is in the form of a slurry. The chemical hydride includes a light metal hydride selected from the group consisting of lithium hydride, lithium borohydride, lithium aluminum hydride, sodium hydride, sodium borohydride, sodium aluminum hydride, magnesium hydride, and calcium hydride. The dispersant comprises a triglyceride.
U.S. Pat. No. 6,733,725 to Zaluska et al describes hydrogen storage compositions derived from an AlH3-based complex hydride incorporating a member selected from a metalloid such as B, C, Si, P and S, a metal such as Cr, Mn, Fe, Co, Ni, Cu, Mo, Zn, Ga, In and Sn, or a metal which forms a stable hydride such as Be, Mg, Ca, Ti, V, Y, Zr and La and a second AlH3-based complex hydride.
U.S. Pat. No. 6,645,651 to Hockaday et al. describes a system of two fuel ampoules that can deliver hydrogen gas as a fuel for small hydrogen fuel cells. Hydrides such as LiH, NaH, NaBH4 CaH2 and LiAlH4, are described as the hydrogen source and co-reactants are selected from water, alcohols, organic and inorganic acids (e.g. acetic acid, sulfuric acid), aldehydes, ketones, esters, nitrites and superacids (e.g. polyoxotungstates), and combinations thereof. A silicone rubber permeable membrane may be employed if required based on the co-reactant.
U.S. Pat. No. 5,305,714 to Sekiguchi et al. describes a fuel supply system for a hydrogen gas engine, having a metal hydride tank in which pellets or powders of a metal hydride absorbing and storing alloy are stored. The alloy may be a Ni—La alloy, a Ti—Mn alloy, a Ti—Fe alloy, a Mg—Ni alloy or a Mg—Mn alloy. The metal hydride alloy powders may be impregnated with a silicone oil to avoid scattering of the metal hydride powder particles.
However, none of these references discloses or suggests a method to stabilize metal borohydride salts, especially highly reactive, pyrophoric and volatile borohydrides, which may render the stabilized composition available for use as a fuel or hydrogen generator.